Medium stacking device and image forming apparatus

ABSTRACT

A medium stacking device includes a medium stacking part stacking a medium, and a first movement part movably provided with respect to the medium stacking part. The first movement part has a first medium restriction part restricting a position of the medium, and a first movement restriction parts including a plurality of restriction members, each of which engaging with the medium stacking part and restricting a direction of the movement of the first movement part.

CROSS REFERENCE TO RELATED APPLICATION

The present application is related to, claims priority from and incorporates by reference Japanese Patent Application No. 2011-181664, filed on Aug. 23, 2011.

TECHNICAL FIELD

The present invention relates to an image forming apparatus, especially relates to a configuration of a medium stacking device including a guide for a medium to be stacked.

BACKGROUND

Conventionally, in such a medium stacking device, in order to regulate a position of a sheet in a width direction which is orthogonal to a carrying direction of the stacked sheet, two sheet guides have been disposed at the left and right of the sheet (see JP Laid-Open Patent Application No. H8-034525 (page 3, FIG. 1).

However, since the conventional sheet guide cannot completely prevent an incline of the guided medium, the medium is sometimes inclined with respect to the carrying direction. One of objects of the present invention is to eliminate the above mentioned problems by a simple configuration.

SUMMARY

A medium stacking device of the present invention includes a medium stacking part stacking a medium, and a first movement part movably provided with respect to the medium stacking part. The first movement part has a first medium restriction part restricting a position of the medium, and a first movement restriction part including a plurality of restriction members, each of which engaging with the medium stacking part and restricting a direction of the movement of the first movement part.

According to the present invention, the first movement part can minimize the incline of the medium which is being carried.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of a main part configuration viewed from the front surface of an image forming apparatus of a first embodiment employing a medium stacking device according to the present invention.

FIG. 2 is a configuration diagram viewed from the front surface (Y axis plus side) of a manual feed tray in the first embodiment.

FIG. 3 is an external perspective view illustrating the configuration of the medium stacking device in the first embodiment.

FIG. 4 is a configuration diagram viewed from the lower side of the medium stacking device in the first embodiment.

FIG. 5 is an external perspective view illustrating a configuration of the surface (upper surface) of a medium stacking plate of the medium stacking device.

FIG. 6 is an external perspective view illustrating a configuration of the rear surface (lower surface) of the medium stacking plate.

FIG. 7 is an external perspective view illustrating a configuration of a sheet guide illustrated in FIG. 3 in the first embodiment.

FIG. 8 is a diagram excluding the medium stacking plate from the configuration diagram of FIG. 4 in the first embodiment.

FIG. 9 is a K-K cross-sectional view illustrating a cross-section along a position passing a center of screws illustrated in FIG. 4 in the first embodiment.

FIG. 10 is a size explanation diagram illustrating a position relationship between the sheet guide installed to the medium stacking plate and a pinion gear rotatably axially fixed to the medium stacking plate in the first embodiment.

FIG. 11A is a partially enlarged diagram for explaining an engagement position with a mesh of the pinion gear and a rack as an example in the first embodiment. FIG. 11B is a diagram illustrating another example of a mesh of the pinion gear and the rack in the first embodiment.

FIG. 12 is a diagram used to an operation explanation of the sheet guide of the medium stacking device stacking recording sheets in the first embodiment.

FIG. 13 is a configuration diagram viewed from the lower side of the medium stacking device in the second embodiment according to the present invention.

FIG. 14 is an M-M cross-sectional view illustrating a cross-section along a position passing a center of screws shown in FIG. 13. The upper side of the medium stacking device is placed up.

FIG. 15 is a diagram used to an operation explanation of the sheet guide of the medium stacking device stacking recording sheets in the second embodiment.

FIG. 16 is a configuration diagram of the medium stacking device viewed from the lower side in the third embodiment according to the present invention.

FIG. 17 is an external perspective view illustrating a configuration of a sheet guide in the third embodiment.

FIG. 18 is an external perspective view illustrating a configuration of a sheet guide in the fourth embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS First Embodiment

In FIG. 1, a sheet tray 51 is disposed, and a sheet feeding part 30 is provided in a sheet feeding side of the sheet tray 51 in the lower part of an image forming apparatus 1 having a configuration as an electrographic printer. Recording sheets 52 are stacked in the sheet tray 51, and the sheet feeding part 30 feeds the recording sheets 52 as a media one by one. A pickup roller 31, a feed roller 32, and a separation piece 33 are provided in the sheet feeding part 30. The pickup roller 31 is provided so as to be contacted and pressed against the recording sheets 52 stacked to a certain height. The feed roller 32 and the separation piece 33 separate the recording sheets 52 fed by the pickup roller 31 one by one.

A manual feed tray 300 is provided with a medium stacking device 302, a pickup roller 303, a feed roller 304 and a retard roller 305. The recording sheets 370 (FIG. 2) are stacked on the medium stacking device 302. The pickup roller 303 is provided so as to be contacted and pressed against a contact part 311 (FIG. 2) of a medium stacking plate 310 of the medium stacking device 302. The feed roller 304 and the retard roller 305 separate the sheets one by one fed by the pickup roller 303. The recording sheets 370 on the medium stacking device 302 are fed to the feed roller 304 by rotation of the pickup roller 303 by drive of motor (not shown), are separated one by one by the feed roller 304 and the retard roller 305, and are sent to a sheet carrying part 40.

The sheet carrying part 40 carries each of the recording sheets 52 that are separated into a sheet and fed from the sheet feeding part 30 to an image forming part 10 via carrying roller pairs 41, 42, and carries the recording sheets 370 (FIG. 2) separated into a sheet and fed from the manual feed tray 300 via the carrying roller pair 42 to the image forming part 10 in the same manner. The image forming part 10 includes four toner image forming parts 11K, 11Y, 11M, 11C (if not necessary to be especially distinguished, may merely be referred to as a toner image forming part 11) sequentially and tandemly arranged from the upstream side of the carrying direction of the recording sheets 52, 370 and, a transfer part 13 transferring a toner image formed by the toner image forming part 11 on the upper surface of the sheet by Coulomb force.

The toner image forming part 11K forms a black (K) toner image. The toner image forming part 11Y forms a yellow (Y) toner image. The toner image forming part 11M forms a magenta (M) toner image. The toner image forming part 11C forms a cyan (C) toner image. In each toner image forming part 11, the photosensitive drum 12 is charged by a charging roller (not shown), image data is written on the rotating photosensitive drum 12 by a light head (not shown), and the image data is developed with toner. Thereby, each color of the toner images can be obtained on the photosensitive drum 12.

The transfer part 13 includes a transfer belt 14 carrying the recording sheet 52 carried from the sheet tray 51 or the recording sheet 370 (FIG. 2) carried from the manual feed tray 300 in the arrow direction, and four transfer rollers 15 disposed so as to face each photosensitive drum 12 of each toner image forming part 11 across the transfer belt 14. The transfer part 13 sequentially transfers the toner image to the recording sheet 52, the toner image for each color being formed by Coulomb force on each photosensitive drum 12 corresponding to each toner image forming part 11.

A fuser 20 fixes the toner image transferred on the recording sheets 52, 370 in the transfer part 13 on the recording sheet by heat and pressure. The recording sheets 52, 370 on which the toner image is fixed are ejected on a stacking part 56 on which the printed recording sheets are stacked via a carrying roller pair 53 and an ejection roller pair 54.

Each of the axes of X, Y, and Z, in FIG. 1 are as follows: X axis is the carrying direction when the recording sheet 52 passes the image forming part 10; Y axis is the rotation axial direction of the photosensitive drum 12; and Z axis is the direction orthogonal to the above mentioned axes. In addition, in a case where each of the axes of X, Y, and Z are shown in the other figures mentioned below, the rotation axial directions respectively indicates identical directions. That is, X, Y, and Z axes in each of the figures show disposition directions of description parts in each of figures configuring the image forming apparatus 1 shown in FIG. 1. Note that the image forming apparatus 1 is herein disposed so that Z axis is a substantially vertical direction.

FIG. 2 is a configuration diagram viewed from the front surface (Y axis plus side) of a manual feed tray 300. FIG. 3 is an external perspective view illustrating the configuration of the medium stacking device 302. FIG. 4 is a configuration diagram viewed from the lower side of the medium stacking device 302.

In FIG. 2, a frame 301 of the manual feed tray 300 is fixed to the image forming apparatus 1 main body. The medium stacking device 302 stacking the recording sheets 370 is rotatably held by the frame 301 as mentioned below. Note that parts other than the manual feed tray 300 of the image forming apparatus 1 may referred to as the image forming apparatus 1 main body. The pickup roller 303 is dispose at a position so as to contact the contact part 311 of the medium stacking plate 310 of the medium stacking device 302. The feed roller 304 is rotatably held by the image forming apparatus 1 main body, and is rotated and driven by a drive motor (not shown). An idler gear 306 links the pickup roller 304 to the feed roller 303. The retard roller 305 is linked to a torque limiter (not shown). A spring 308 biases the retard roller 305 toward the feed roller 304. A spring 309 biases the medium stacking device 302 toward a direction in which the contact part 311 of the medium stacking device 302 contact pickup roller 303.

Note that the manual feed tray 300 herein, for example, includes the frame 301, the medium stacking device 302, the pickup roller 303, the spring 309, and the idler gear 306.

As shown in FIG. 3 and FIG. 4, the medium stacking device 302 includes the medium stacking plate 310 as a medium stacking part, a sheet guide 320 as a first movement part, a sheet guide 321 as a second movement part, a pinion gear 381 as a first gear part, and a pinion gear 382 as a second gear part. A pair of posts 335, 336 formed on both of end parts of the medium stacking plate 310 are respectively inserted into guide grooves 301 a, 301 b (FIG. 2) formed on the frame 301. Thereby, the medium stacking device 302 is rotatably held. Furthermore, as mentioned above, the contact part 311 of the medium stacking device 302 is biased in the direction where the contact part 311 contacts the pickup roller 303 by the spring 309. The pinion gears 381 and 382 are positioned along in the medium carrying direction and at a substantially middle of the sheet guides 320 and 321.

FIG. 5 is an external perspective view illustrating a configuration of the surface (upper surface) of a medium stacking plate 310 of the medium stacking device 302. FIG. 6 is an external perspective view illustrating a configuration of the rear surface (lower surface) of the medium stacking plate 310.

As shown in FIG. 5 and FIG. 6, a center plate part 340 is formed in a center part of the medium stacking plate 310, and extends in a direction of arrow A (vertical to Y axis, however not always vertical to Z axis) indicating a carrying direction of the stacked recording sheets 370 (FIG. 2). Guide grooves 331, 332, 333, 334 are alternately formed from both sides of the center plate part 340. The guide grooves extend in a width direction (Y axis direction) of the stacked recording sheets. An insertion part 331 a, 332 a, 333 a, 334 a is formed in each guide groove 331-334. The insertion parts 331 extend outward only a predetermined width in both directions which are orthogonal each other in a position close to the center plate part 340. All of the guide grooves 331-334 and the insertion parts 331 a-334 a penetrate to the rear side of the medium stacking plate 310 as shown in FIG. 6.

FIG. 7 is an external perspective view illustrating a configuration of a sheet guide 320 illustrated in FIG. 3. Note that since the configuration of the sheet guide 321 herein is identical to that of the sheet guide 320, the configuration will be explained with reference to the sheet guide 320.

The sheet guide 320 includes a guide block 350 extending in the direction of arrow A along which the stacked recording sheets are carried, and a pair of racks 355, 356 as a first movement restriction part extending in the width direction (Y axis direction) of the recording sheet. A restriction surface 351 as a first medium restriction part and a stacking surface 352 a are formed in the guide block 350. The restriction surface 351 that is vertical surface with respect to Y axis, extends in the direction of arrow A, and restricts a position of the width direction of the recording sheet. The stacking surface 352 a that is orthogonal to the restriction surface 351 extends in the direction of arrow A. The edges of the width direction of the recording sheets are stacked on the stacking surface 352 a. Note that a pair of racks 355, 356 of the sheet guide 321 corresponds to a second movement restriction part. The restriction surface 351 of the sheet guide 321 corresponds to a second medium restriction part. In this embodiment, each of the movement restriction parts is realized with two restriction members (racks 355 and 356). The number of the restriction members for one movement restriction part is preferably two, but may be three or more.

Rack holding members 353, 354 respectively holding the racks 355, 356 are formed below a plate-shaped part 352. The upper surface of the plate-shaped part 352 is the stacking surface 352 a. The each rack 355, 356 projects downward from the lower surface of the plate-shaped part 352 so that the upper surface of each rack 355, 356 and the lower surface of the plate-shaped part 352 have a predetermined interval g. As shown in FIG. 7, the racks 355, 356 have the predetermined interval between them, and are formed at a position where the racks shifted in the direction of arrow A with respect to a width center of the guide block 350. The position relationship of these will be explained below.

The rack 355 and the rack 356 are plate-shaped members having flat surfaces in parallel to the stacking surface 352 a. The racks 355 and the rack 356 are formed vertically with respect to the restriction surface 351, and have a substantially identical shape, and are formed in parallel. A restriction part 355 b and a restriction part 356 b are formed in one edge of the guide block side of the rack 355 and the rack 356. A restriction part 355 f and a restriction part 356 f are formed in the other edge of the guide block side of the rack 355 and the rack 356. In addition, in the opposite side of arrow A of the rack 355 and the rack 356, a tooth part 355 d and a tooth part 356 d are formed between both of the restriction parts, and in the arrow A side, a pair of bias parts 355 c, 355 e and a pair of bias parts 356 c, 356 e are formed in the neighborhood of both of the restriction parts.

As shown in FIG. 3 and FIG. 4, the rack holding members 353, 354 of the sheet guide 320 are installed to the medium stacking plate 310 so that the rack holding members 353, 354 are respectively guided to the guide grooves 333, 331 of the medium stacking plate 310. The rack holding members 353, 354 of the sheet guide 321 are installed to the medium stacking plate 310 so that the rack holding members 353, 354 are respectively guided to the guide grooves 332, 334 of the medium stacking plate 310. Installation method of the guide grooves will be explained hereinafter.

Here, the case where the sheet guide 320 shown in FIG. 7 is installed to the medium stacking plate 310 shown in FIG. 5 and FIG. 6 will be explained. First, the sheet guide 320 is rotated substantially 90 degrees around X axis in a direction of arrow B. Respectively, a front edge of the restriction part 355 f of the rack 355 is inserted in a direction of arrow C (FIG. 5) so that the front edge is substantially vertically inserted into the insertion part 333 a of the guide groove 333 of the medium stacking plate 310. In addition, a front edge of the restriction part 356 f of the rack 356 is inserted in a direction of arrow C (FIG. 5) so that the front edge is substantially vertically inserted into the insertion part 331 a of the guide groove 331 of the medium stacking plate 310. The sheet guide 320 is pushed and entered until the plate-shaped part 352 abuts on the upper surface of the medium stacking plate 310.

For this reason, the width of the insertion part 333 a is made to be wider than each width Wa1, Wa2 of the restriction parts 355 b, 355 f. In addition, the width of the insertion part 333 a is made to be wider than each width Wb1, Wb2 of the restriction parts 356 b, 356 f. Furthermore, the width of the rack holding part 353 is made to be narrower than each width Wa1, Wa2 of the restriction parts 355 b, 355 f. The width of the guide groove 333 is formed to have a width suitable for guiding the inserted rack holding member 353. In the same manner, the width of the rack holding part 354 is made to be narrower than each width Wb1, Wb2 of the restriction parts 356 b, 356 f. The width of the guide groove 331 is formed to have a width suitable for guiding the inserted rack holding member 354.

At the stage where the plate-shaped part 352 abuts on the upper surface of the medium stacking plate 310, the sheet guide 320 is rotated around X axis in the opposite direction of a direction of arrow B. Thereby, the rack holding member 353 and the rack holding member 354 is respectively inserted into to the guide groove 333 and the guide groove 331, and the rack 355 and the rack 356 respectively extends in parallel via the medium stacking plate 310 on the lower surface of the medium stacking plate 310. Furthermore, until the guide block 350 is positioned at one end side of the medium stacking plate 310, the sheet guide 320 is guided and moved by the guide grooves 333, 331. Thereby, the sheet guide 320, for example, as shown in FIG. 3, is placed at an initial position. The initial position mentioned herein indicates a farthest part position of the sheet guide 321.

In the same manner, a front edge of the restriction part 355 f of the rack 355 of the sheet guide 321 is inserted in a direction of arrow C (FIG. 5) so that the front edge is substantially vertically inserted into the insertion part 332 a of the guide groove 332 of the medium stacking plate 310. In addition, a front edge of the restriction part 356 f of the rack 356 is inserted in a direction of arrow C (FIG. 5) so that the front edge is substantially vertically inserted into the insertion part 334 a of the guide groove 334 of the medium stacking plate 310. Until the guide block 350 is positioned at another end side of the medium stacking plate 310, the sheet guide 321 is guided and moved by the guide grooves 332, 334. Thereby, the sheet guide 321, for example, as shown in FIG. 3, is placed at the initial position.

As shown in FIG. 4 and FIG. 6, the guide wall 341 a and the guide wall 341 b are formed on the lower surface of the medium stacking plate 310. The guide wall 341 a faces the bias parts 356 c, 356 e of the rack 356 of the sheet guide 320. The guide wall 341 b faces the abutment parts 356 a, 356 g of the rack 356 of the sheet guide 320. The abutment parts 356 a, 356 g receive bias force from the bias parts 356 c, 356 e, contact the guide wall 341 b, and guide the movement of the rack 356 of the sheet guide 320 without shaking the sheet guide. In the same manner, the guide wall 342 a and the guide wall 342 b are formed on the lower surface of the medium stacking plate 310. The guide wall 342 a faces the bias parts 355 c, 355 e of the rack 355 of the sheet guide 320. The guide wall 342 b faces the abutment parts 355 a, 355 g of the rack 355 of the sheet guide 320. The abutment parts 355 a, 355 g receive bias force from the bias parts 355 c, 355 e, contact the guide wall 342 b, and guide the movement of the rack 355 of the sheet guide 320 without shaking the sheet guide. The guide walls 341 a and 341 b functions as support parts for the abutment parts 356 a and 356 g. The support parts function to allow the first and second medium restriction parts to move in predetermined directions. In the embodiments, the abutment parts 355 a, 355 g of the rack 355 contact the guide walls 341 a, 341 b, and slidably move along the surfaces of the guide walls 341 a, 341 b. As long as the support parts allows the medium restriction parts to move without shaking the sheet guide, there is no structural or material restriction for the support parts. For example, the support part may have a curved surface other than the plane surface. The support part may have a projection shape which protrudes toward the abutment part and of which a tip contacts the abutment part so that the movement of the abutment part is restricted by the tip of the support part.

In the same manner, the guide wall 344 a and the guide wall 344 b are formed on the lower surface of the medium stacking plate 310. The guide wall 344 a faces the bias parts 356 c, 356 e of the rack 356 of the sheet guide 321. The guide wall 344 b faces the abutment parts 356 a, 356 g of the rack 356 of the sheet guide 321. The abutment parts 356 a, 356 g receive bias force from the bias parts 356 c, 356 e, contact the guide wall 344 b, and guide the movement of the rack 356 of the sheet guide 321 without shaking the sheet guide. In the same manner, the guide wall 343 a and the guide wall 343 b are formed on the lower surface of the medium stacking plate 310. The guide wall 343 a faces the bias parts 355 c, 355 e of the rack 355 of the sheet guide 321. The guide wall 343 b faces the abutment parts 355 a, 355 g of the rack 355 of the sheet guide 321. The abutment parts 355 a, 355 g receive bias force from the bias parts 355 c, 355 e, contact the guide wall 343 b, and guide the movement of the rack 355 of the sheet guide 321 without shaking the sheet guide.

FIG. 8 is a diagram excluding the medium stacking plate 310 from the configuration diagram of FIG. 4 in the first embodiment. FIG. 9 is a K-K cross-sectional view illustrating a cross-section along a position passing a center of screws 345, 346 illustrated in FIG. 4.

As shown in FIG. 8, the sheet guide 320 and the sheet guide 321 have a substantially identical shape. When the sheet guides are installed to the medium stacking plate 310 and each the sheet guide is at the initial position, in the direction of arrow A that is the moving direction of the recording sheet, the racks 355, 356 of each sheet guide alternately are disposed in parallel at a predetermined interval. Especially, the tooth part 355 d of the sheet guide 320 is adjacent to the tooth part 356 d of the sheet guide 321 and the tooth part 356 d of the sheet guide 320 is adjacent to the tooth part 355 d of the sheet guide 321. One part of a region of each of front edge sides of the tooth parts adjacent to each other face at a predetermined interval in the center part of the width direction (Y axis direction) of the recording sheet 370 of the medium stacking plate 310.

As shown in FIG. 8, the pinion gear 381 and the pinion gear 382 are respectively disposed in the center part of the width direction of the recording sheet 370 of the medium stacking plate 310 at a position where the tooth part 356 d of the sheet guide 320 and the tooth part 355 d of the sheet guide 321 face, and a position where the tooth part 355 d of the sheet guide 320 and the tooth part 356 d of the sheet guide 321 face. The pinion gear 381 and the pinion gear 382 are respectively rotatably fixed at the medium stacking plate 310 by the screw 345 and the screw 346.

As shown in FIG. 9, the tooth part 381 a and a flange part 381 b are formed in the pinion gear 381. The tooth part 381 a meshes with the tooth part 356 d of the rack 356 of the sheet guide 320 and with the tooth part 355 d of the rack 355 of the sheet guide 321. The flange part 381 b projects so as to cover each part of the rack 356 of the sheet guide 320 and the rack 355 of the sheet guide 321. In the same manner, the tooth part 382 a and a flange part 382 b are formed in the pinion gear 382. The tooth part 382 a meshes with the tooth part 356 d of the rack 356 of the sheet guide 321 and with the tooth part 355 d of the rack 355 of the sheet guide 320. The flange part 382 b projects so as to cover each part of the rack 356 of the sheet guide 321 and the rack 355 of the sheet guide 320. Note that, in FIGS. 4, 8, only each pitch circle (standard circle) 381 p, 382 p of each tooth part 381 a, 382 a of the pinion gear 381, 382 are shown by dotted lines.

The plate-shaped part 352 of the guide block 350 of the sheet guide 320 installed to the medium stacking plate 310 is restricted by the medium stacking plate 310. In addition, the racks 355, 356 of the sheet guide 320 are restricted by each of the flange parts 381 b, 382 b of the pinion gears 381, 382. Accordingly, the sheet guide 320 is not detached below (here, the minus side of Z axis). In addition, since the widths of the racks 355, 356 are respectively formed wider than the widths of the guide grooves 331, 333 of the medium stacking plate 310. Accordingly, the sheet guide 320 is not detached above (here, plus side of Z axis). In the same manner, the sheet guide 321 installed to the medium stacking plate 310 is configured so as not to detach in upper and lower directions with respect to the medium stacking plate 310.

Note that, as shown in FIG. 9, a wave washer 383 is arranged in a compressed manner between the pinion gear 382 and the medium stacking plate 310, and biases the pinion gear 382 toward the screw 346. This wave washer 383 adjusts a rotation load of the pinion gear 382, and thereby, adjusts the movement load of the sheet guides 320, 321. The wave washer 383 may respectively be provided to the two pinion gears 381, 382. However, here, as described below since two of the pinion gears 381 and 382 link each other, the wave washer 383 may provided only to the pinion gear 382.

As shown in FIG. 4 (see FIG. 8), the abutment parts 356 a, 356 g of the sheet guide 320 contact the guide wall 341 b of the medium stacking plate 310 by bias from the bias parts 356 c, 356 e, and restrict an mesh position of the pinion gear 381 and the rack 356 as well as a movement range of the sheet guide 320 with respect to the medium stacking plate 310. In the same manner, the abutment parts 355 a, 355 g of the sheet guide 320 contact the guide wall 342 b of the medium stacking plate 310 by bias from the bias parts 355 c, 355 e, and restrict an mesh position of the pinion gear 382 and the rack 355 as well as a movement range of the sheet guide 320 against the medium stacking plate 310.

Meanwhile, the abutment parts 356 a, 356 g of the sheet guide 321 contact the guide wall 344 b of the medium stacking plate 310 by bias from the bias parts 356 c, 356 e, and restrict an mesh position of the pinion gear 382 and the rack 356 as well as a movement range of the sheet guide 321 with respect to the medium stacking plate 310. In the same manner, the abutment parts 355 a, 355 g of the sheet guide 321 contact the guide wall 343 b of the medium stacking plate 310 by bias from the bias parts 355 c, 355 e, and restrict an mesh position of the pinion gear 381 and the rack 355 as well as a movement range of the sheet guide 321 against the medium stacking plate 310.

FIG. 10 is a size explanation diagram illustrating a position relationship between the sheet guides 320, 321 installed to the medium stacking plate 310 and the pinion gears 381, 382 rotatably axially fixed to the medium stacking plate 310. Note that, here, for the sake of convenience, “′” are putted to the reference numbers of each configuration element of the sheet guide 321, to distinguish each configuration element of the sheet guide 320. Note that FIG. 10 corresponds to FIG. 8 the medium stacking device 302 viewed from the lower side (the minus side of Z axis), and the direction of arrow A in FIG. 10 shows the carrying direction of the stacked recording sheet.

As shown in the above figure, the sheet guides 320, 321 have the same identical figure. Restriction surfaces 351, 351′ face each other and extend in the direction of arrow A. And the racks 355, 356 of the sheet guide 320 and the racks 355′, 356′ of the sheet guide 321 are disposed so as to be alternately positioned in the direction of arrow A. Furthermore, the pinion gear 381 is disposed so as to mesh with each of the racks between the rack 356 of the sheet guide 320 and the rack 355′ of the sheet guide 321 extending each other in parallel. The pinion gear 382 is disposed so as to mesh with each of the racks between the rack 355 of the sheet guide 320 and the rack 356′ of the sheet guide 321.

A length in the direction of arrow A of the guide block 350 (350′) is defined as L. A diameter of each pitch circle (standard circle) 381 p, 382 p of each pinion gear 381, 382 disposed in line in direction of arrow A is defined as d. A position relationship between the rack 355 (355′) and the rack 356 (356′) extending in parallel to the rack 355 will be explained.

A hypothetical center line being the perpendicular bisector between each of rotation centers 381 c, 382 c of the pinion gears 381, 382 and extending in a width direction (Y axis direction) of the stacked recording sheet is defined as P. A distance from the hypothetical center line P to the rotation center 381 c is defined as X. A distance from the hypothetical center line P to the rotation center 382 c is defined as X.

At this time, a distance from the hypothetical center line P to a pitch line (standard line) 355 p′ of the rack 355′ being an engagement position of the pinion gear 381 is defined as Z. The distance Z is obtained by the following Formula:

Z=X−d/2.

The tooth part 355 d (FIG. 8) is formed so that this position is a pitch line (standard line) 355 p′ of the rack 355′. In addition, a distance from the pitch line (standard line) 355 p′ of the rack 355′ to a pitch line (standard line) 356 p′ of the rack 356′ being the engagement position with the pinion gear 382 is defined as Y. The distance Y is obtained by the following Formula:

Y=2X.

The tooth part 356 d (FIG. 8) is formed so that this position is a pitch line (standard line) 356 p′ of the rack 356′.

In addition, with respect to the restriction surface 351′ having the length L in the direction of arrow A, the substantially center in the direction of arrow A of the restriction surface 351′ is disposed so as to coincide with the hypothetical central line P, and at least one of the racks 355′, 356′ is disposed in the direction of arrow A side (downstream side) and the opposite side of the direction of arrow A side (upstream side) based on the substantially center. Note that, in the drawing, rack 355′ on the downstream side, rack 356′ on the upstream side. In this case, obviously shown in the arrangement in FIG. 10, when a width of the rack 355′ is defined as w1, and a width of the rack 356′ is defined as w2, Z and K are necessary to be set by the following formulae:

Z>w1, and

K=L/2−(Z+d)>w2.

By forming in this manner, the sheet guide 320 and the sheet guide 321 having the same shape can be disposed and face each other, can be installed to the medium stacking plate 310.

Note that, here, the substantially center in the direction of arrow A of the restriction surface 351′ is disposed so as to coincide with the hypothetical central line P. However, if the substantially center mentioned herein indicates the hypothetical center line P being included in a region having a length of L/2±20%, same effects can be obtained by the arrangement of the line P.

In addition, the engagement position mentioned herein is a position where the pinion gear 381 meshes with the racks 355′, 356, and the pinion gear 382 meshes with the racks 355, 356′. FIGS. 11A and 11B are partially enlarged diagrams for explaining an engagement position with a mesh of the pinion gear 381 and the rack 355′ as an example.

As shown in FIG. 11A, the pinion gear 381 and the rack 355′ are engaged so that one of tangential lines of the pitch circle (standard circle) 381 p of the pinion gear 381 is positioned in the substantially center of a range h2 from an addendum to a dedendum of the tooth part 355 d′ of the rack 355′. A position on the rack 355′ where the pitch circle (standard circle) 381 p of the pinion gear 381 contacts in this way corresponds to the pitch line (standard line) 355 p′ of the rack. Accordingly, the engagement position mentioned herein corresponds to a position where the pitch circle (standard circle) of the pinion gear contacts the pitch line (standard line) of the rack.

The above mentioned engagement position is merely one example. The engagement position may be a position in a region where a range h1 and the range h2 intersect. The range h1 is from the addendum to the dedendum of the tooth part 381 a of the pinion gear 381. The range h2 is from the addendum to the dedendum of the tooth part 355 d′ of the rack 355′. For example, as shown in FIG. 11B, in a case where the pinion gear 381 is shifted, a position relationship causing the pinion gear 325 to engage with the rack 355′ differs from that shown in FIG. 11A. The engagement position of the other pinion gear with the rack is identical to the above mentioned engagement position.

In addition, for example, the tooth part 355 d of the rack 355 and the tooth part 356 d of the rack 356 have the identical pitch and the identical phase viewed from the restriction surface 351 in the sheet guide 320 shown in FIG. 7. The sheet guide 321 is configured in the same manner as mentioned above. In addition, for example, the pinion gear 381 and the pinion gear 382 shown in FIG. 8, have the identical number of teeth, and as shown in FIG. 11, the number herein is 16, which is even number. Furthermore, the pinion gears respectively include the flange parts 381 b, 382 b, and have the identical module.

In the above mentioned configuration, operation of the sheet guides 320, 321 in the medium stacking device 302 of the manual feed tray 300 will be explained with reference to FIG. 12. Note that FIG. 12 is a diagram used to an operation explanation of the sheet guides 320, 321 of the medium stacking device 302 stacking recording sheets 370. In the above figure, only a region in the recording sheet 370 where the medium stacking device exists is specified by drawing with diagonal lines.

Firstly, the medium stacking device 302 is pushed down against bias of the spring 309 by an operation device (not shown), so that the contact part 311 of the medium stacking device 302 shown in FIG. 2 is separated only at a predetermined interval from the pickup roller 303, and the medium stacking device 302 is restricted at the position where the medium stacking device 302 is pushed down. In the state where the medium stacking device 302 is pushed down in this way, the recording sheets 370 are placed on the manual feed tray 300. At this time, the sheet guide 320 and the sheet guide 321 are moved to outside and the recording sheets 370 are stacked on the medium stacking device 302 so that the width direction edges of the recording sheet 370 are positioned on each of the stacking surfaces 352 a of the sheet guide 320 and the sheet guide 321. Each of the restriction surfaces 351 of the sheet guides 320 and 321 are moved in a center direction until the restriction surfaces 351 abut on end surfaces of the recording sheets 370.

At this time, each of the restriction surfaces 351 of the sheet guide 320 and the sheet guide 321 are symmetrically moved away from and toward a line connecting each of the rotate center s of the pinion gears 381 and 382 (see FIG. 8) as the center line. Accordingly, when the guide block 350 of either the sheet guide 320 or sheet guide 321 is moved, the other guide block 350 is also symmetrically moved via the pinion gears. Thereby, the width direction position of the recording sheet 370 can be restricted.

As mentioned above, since the tooth part 355 d of the rack 355 and the tooth part 356 d of the rack 356 are configured to have the identical pitch and the identical phase viewed from the restriction surface 351, and the pinion gear 381 and the pinion gear 382 have the identical shape, even if a rack and pinion is configured with the two racks 355, 356 in this way, sliding motion can be smoothly performed.

After determination of a position of the width direction of the recording sheet 370 on the medium stacking device 302 is performed as mentioned above, position restriction by an operation device (not shown) is unlocked, and as shown in FIG. 2, the top sheet of the stacked recording sheets 370 contacts the pickup roller 303 by bias force of the spring 309. In such a state, the pickup roller 303 activates and the recording sheet 370 is fed, the recording sheet 370 is fed in the direction of arrow A in FIG. 12. At this time, the recording sheet 370 may skew in a rotation direction of either arrow Ma or arrow Mb.

For example, when the recording sheet 370 skews in the direction of arrow Ma, the rear edge side in the direction of arrow A of the restriction surface 351 of the sheet guide 321 receives a pressure force Fa from the recording sheet 370 generated by skew, and the front edge side in the direction of arrow A of the restriction surface 351 of the sheet guide 320 receives a pressure force Fc from the recording sheet 370 generated by skew. At this time, a movement force Fd is generated at the front edge side of the sheet guide 321 toward the center direction to rotate in the direction of arrow Mc, a movement force Fb is generated at the rear edge side of the sheet guide 320 toward the center direction to rotate in the direction of arrow Md.

At this time, the movement force Fd, which is generated at the front edge side of the sheet guide 321, is led to the front edge side of the sheet guide 320 via the rack 355′ of the sheet guide 321, the pinion gear 381, the rack 356 of the sheet guide 320 shown in FIG. 10, and reaches the front edge side of the sheet guide 320 as a force cancelling the pressure force Fc from the recording sheet 370. In the same manner, the movement force Fb, which is generated at the rear edge side of the sheet guide 320, is led to the rear edge side of the sheet guide 321 via the rack 355 of the sheet guide 320, the pinion gear 382, the rack 356′ of the sheet guide 321 shown in FIG. 10, and reaches the rear edge side of the sheet guide 320 as a force cancelling the pressure force Fa from the recording sheet 370.

In a case where the recording sheet 370 skews in the direction of arrow Mb, in the same manner, a pressure force which each sheet guide 320, 321 respectively receives from the recording sheet 370 is cancelled.

As mentioned above, according to the medium stacking device of the embodiment, since the pinion gears 381, 382 arranged at the positions being separated in the direction of arrow A respectively link to the racks extending from the sheet guides 320, 321, even if skew is generated in the carried recording sheet, an incline of the sheet guides 320, 321 is suppressed, and the skew of the recording sheet can be diminished.

Second Embodiment

FIG. 13 is a configuration diagram viewed from the lower side (the minus side of Z axis) of the medium stacking device 402 in the second embodiment according to the present invention. FIG. 14 is an M-M cross-sectional view illustrating a cross-section along a position passing a center of screws 345, 346 shown in FIG. 13. The upper side of the medium stacking device 402 is placed up in FIG. 4.

The image forming apparatus employing this medium stacking device 402 has main different points from the image forming apparatus employing the above mentioned medium stacking device 302 of the first embodiment shown in FIG. 4. The points are that, for example, upper layer gears 481 d, 482 d are added to the pinion gears 481, 482 (381, 382 in embodiment 1) and the pinion gears are formed as a two stage gear, and that an idler gear 400 meshing with these upper gears 481 d, 482 d is added. In the invention, a transferring part means a part that functions to convey a power from the first gear part to the second gear part. In this embodiment, the transferring part is configured with the upper layer gears 481 d, 482 d and idler gear 400. As long as the transferring part is able to convey the power from the first gear part to the second gear part, there is no structural restriction. The number of parts, gears for the transferring part vary according to the configuration. Instead of the mechanical structure by gears discussed above, friction force or magnetic force may be useful to realized the transferring part.

Accordingly, the same reference numbers are put to, and explanation and figures are omitted for parts of the image forming apparatus employing this medium stacking device 402 that are common with the image forming apparatus 1 of the first embodiment mentioned above (FIG. 1). Different parts of the image forming apparatus from those of the image forming apparatus 1 are intensively explained. Note that since the main configuration of the image forming apparatus of the embodiment is common with the main configuration of the image forming apparatus 1 of the first embodiment shown in FIG. 1 other than the medium stacking device 402, FIGS. 1, 2 will be referred if needed.

In FIG. 13 and FIG. 14, in the pinion gears 481, 482, not only the first stage gear meshing with each rack, as explained in the first embodiment, but also the upper layer gears 481 d, 482 d being a second stage gear are formed via flange parts 481 b, 482 b. In FIG. 13, pitch circles of the upper layer gears 481 d, 482 d are shown. The idler gear 400 is disposed in the center part of these pinion gears 481,482, and is rotatably fixed in the center point between axes of the pinion gears 481, 482 by a screw 401 to medium stacking plate 310. In FIG. 13, a pitch circle 400 p of the idler gear 400 is shown by dotted lines.

As shown in FIG. 14, a wave washer 405 is arranged in a compressed manner between the idler gear 400 and the medium stacking plate 310 and, biases the idler gear 400 toward the screw 401. Note that a notch part 455 h for allowing attachment of the idler gear 400 to the medium stacking plate 310 is formed in a rack 455 (355 in the first embodiment) of the sheet guides 420, 421 (320, 321 the first embodiment).

The idler gear 400 respectively meshes with each upper layer gear 481 d, 482 d of these pinion gears 481, 482 at the center parts of the pinion gears 481, 482 and causes the pinion gear 481 to link to the pinion gear 482.

Note that, here, the sheet guide 420 corresponds to a first movement part. The sheet guide 421 corresponds to a second movement part. The pair of racks 455, 456 of the sheet guide 420 corresponds to a first movement restriction part. The pair of racks 455, 456 of the sheet guide 421 corresponds to a second movement restriction part. The restriction surface 351 of the sheet guide 420 corresponds to a first medium restriction part. The restriction surface 351 of the sheet guide 421 corresponds to a second medium restriction part.

In the above mentioned configuration, operation of the sheet guide 420, 421 in the medium stacking device 402 of will be explained with reference to FIG. 15. Note that FIG. 15 is a diagram used to an operation explanation of the sheet guides 420,421 of the medium stacking device 402 stacking the recording sheets 370. In the above figure, only a region in the recording sheet 370 where the medium stacking device exists is specified by drawing with diagonal lines.

Firstly, the medium stacking device 402 is pushed down against bias of the spring 309 by an operation device (not shown), so that the contact part 311 of the medium stacking device 302 shown in FIG. 2 (herein referred to as 402) is separated only at a predetermined interval from the pickup roller 303, and the medium stacking device 402 is restricted at the position where the medium stacking device 402 is pushed down. In the state where the medium stacking device 402 is pushed down in this way, the recording sheets 370 are placed on the manual feed tray 300. At this time, the sheet guide 420 and the sheet guide 421 are moved to outside and the recording sheets 370 are stacked on the medium stacking device 402 so that the width direction edges of the recording sheet 370 are positioned on each of the stacking surfaces 352 a of the sheet guide 420 and the sheet guide 421. Each of the restriction surfaces 351 of the sheet guides 420 and 421 are moved in a center direction until the restriction surfaces 351 abut on end surfaces of the recording sheets 370.

At this time, each of the restriction surfaces 351 of the sheet guide 420 and the sheet guide 421 are symmetrically moved away from and toward and a line connecting each of the rotate centers of the pinion gears 481 and 482 (see FIG. 13) as the center line. At this time, the pinion gear 481 and the pinion gear 482 simultaneously rotate in the identical direction with the movement of the sheet guide 420 and the sheet guide 421, while the idler gear 400 links these gears rotating in the opposite direction. As mentioned above, in the case where the idler gear 400 is added, even the two racks 455,456 are used to configure the rack and pinion, sliding motion can be smoothly performed.

Thereby, after determination of a position of the width direction of the recording sheet 370 on the medium stacking device 402 is performed as mentioned above, position restriction by an operation device (not shown) is unlocked and as shown in FIG. 2, the top sheet of the stacked recording sheets 370 contacts the pickup roller 303 by bias force of the spring 309. In such a state, the pickup roller 303 activates and the recording sheet 370 is fed, the recording sheet 370 is fed in the direction of arrow A in FIG. 15. At this time, the recording sheet 370 may skew in a rotation direction of either arrow Ma or arrow Mb.

For example, when the recording sheet 370 skews in the direction of arrow Ma, the rear edge side in the direction of arrow A of the restriction surface 351 of the sheet guide 421 receives the pressure force Fa from the recording sheet 370 generated by skew. At this time, the front edge side of the sheet guide 420 generates the movement force Fd toward the center direction to rotate in the direction of arrow Mc.

These forces generated by skew toward the direction of arrow Ma cause the pinion gear 481 and the pinion gear 482 (FIG. 13) to rotate in the opposite direction each other. However, these pinion gear 481 and pinion gear 482 linked by the idler gear 400 cannot rotate in the opposite direction each other. Accordingly, the sheet guide 421 does not rotate in the direction of arrow Ma. In the same manner, in a case where the recording sheet 370 skews toward the direction of arrow Mb, the sheet guide 421 does not rotate in direction of arrow Mb. Since the forces act with respect to the sheet guide 420 in the same manner, the sheet guide 420 and the sheet guide 421 can always keep the respective restriction surfaces 351 in parallel with respect to the direction of arrow A being the sheet carrying direction.

As mentioned above, according to the medium stacking device of the embodiment, since the pinion gears 481, 482 arranged at the positions being separated in the direction of arrow A link to the idler gear 400, even if skew is generated in the carried recording sheet, thereby, since an incline of the sheet guides 420, 421 is suppressed, and the skew of the recording sheet can be diminished.

Third Embodiment

FIG. 16 is a configuration diagram of the medium stacking device 502 viewed from the lower side (the minus side of Z axis) in the third embodiment according to the present invention. FIG. 17 is an external perspective view illustrating a configuration of a sheet guide 520 (521).

The image forming apparatus employing this medium stacking device 502 has a main different point from the image forming apparatus employing the above mentioned medium stacking device 302 of the first embodiment shown in FIG. 4. The point is that instead of the pinion gears 381, 382, the flanges 581, 582 without a gear are fixed by the screws 345, 346 to the medium stacking plate 310, and plate-shaped extending parts 555, 556 are formed instead of the racks in each sheet guide 520, 521. In this embodiment, the movement restriction parts are realized with two restriction members (extending parts 555 and 556). The number of the restriction members for one movement restriction part is preferably two, but may be three or more.

Accordingly, the same reference numbers are put to, and explanation and figures are omitted for parts of the image forming apparatus employing this medium stacking device 502 that are common with the image forming apparatus 1 of the first embodiment mentioned above (FIG. 1). Different parts of the image forming apparatus from those of the image forming apparatus 1 are intensively explained. Note that since the main configuration of the image forming apparatus of the embodiment is common with the main configuration of the image forming apparatus 1 of the first embodiment shown in FIG. 1 other than the medium stacking device 502, FIGS. 1, 2 will be referred if needed.

The extending part 555 of the sheet guide 520 is formed to have a width forming a necessary minimum gap to guide and smoothly slide a side part 555 b and a side part 555 a. The side part 555 b is guided by the guide wall 342 a formed in the medium stack plate 310 and the side part 555 a is guided by the guide wall 342 b formed in the medium stack plate 310. In the same manner, the extending part 556 of the sheet guide 520 is formed to have a width forming a necessary minimum gap to guide and smoothly slide a side part 556 b and a side part 556 a. The side part 556 b is guided by the guide wall 341 a formed in the medium stack plate 310 and the side part 556 a is guided by the guide wall 341 b formed in the medium stack plate 310.

Note that, here, the side parts 555 a, 555 b of the extending part 555 and the side parts 556 a, 556 b of the extending part 556 correspond to an abutment part. The guide walls 341 a, 341 b, 342 a, and 342 b correspond to support parts.

In addition, the extending part 555 of the sheet guide 521 is formed to have a width forming a necessary minimum gap to guide and smoothly slide a side part 555 b and a side part 555 a. The side part 555 b is guided by the guide wall 342 a formed in the medium stack plate 310 and the side part 555 a is guided by the guide wall 343 b formed in the medium stack plate 310. In the same manner, the extending part 556 of the sheet guide 521 is formed to have a width forming a necessary minimum gap to guide and smoothly slide a side part 556 b and a side part 556 a. The side part 556 b is guided by the guide wall 344 a formed in the medium stack plate 310 and the side part 556 a is guided by the guide wall 344 b formed in the medium stack plate 310.

The flange 581 restricts detachment of the extending part 556 of the sheet guide 520 and the extending part 555 of the sheet guide 521 below (here, the minus side of Z axis. The flange 582 restricts detachment of the extending part 555 of the sheet guide 520 and the extending part 556 of the sheet guide 521 below (here, the minus side of Z axis). Accordingly, the respective sheet guide 520 and the sheet guide 521 herein individually move without linking each other.

Note that, here, the sheet guide 520 corresponds to a first movement part. The sheet guide 521 corresponds to a second movement part. The pair of extending parts 555, 556 of the sheet guide 520 corresponds to a first movement restriction part. The pair of racks 555, 556 of the sheet guide 521 corresponds to a second movement restriction part. The restriction surface 351 of the sheet guide 520 corresponds to a first medium restriction part. The restriction surface 351 of the sheet guide 521 corresponds to a second medium restriction part.

In the above mentioned configuration, operation of the sheet guides 520, 521 in the medium stacking device 502 will be explained.

Firstly, the medium stacking device 502 is pushed down against bias of the spring 309 by an operation device (not shown), so that the contact part 311 of the medium stacking device 302 shown in FIG. 2 (herein referred to as 502) is separated only at a predetermined interval from the pickup roller 303, and the medium stacking device 502 is restricted at the position where the medium stacking device 502 is pushed down. In the state where the medium stacking device 502 is pushed down in this way, the recording sheets 370 are placed on the manual feed tray. At this time, the sheet guide 520 and the sheet guide 521 are moved to outside and the recording sheets 370 are stacked on the medium stacking device 502 so that the width direction edges of the recording sheet 370 are positioned on each of the stacking surfaces 352 a of the sheet guide 520 and the sheet guide 521. Each of the restriction surfaces 351 of the sheet guides 520 and 521 are moved in a center direction until the restriction surfaces 351 abut on end surfaces of the recording sheets 370.

At this time, since the sheet guide 520 and the sheet guide 521 do not link each other, they need to be individually moved by a user.

After determination of a position of the width direction of the recording sheet 370 on the medium stacking device 502 is performed as mentioned above, position restriction by an operation device (not shown) is unlocked and as shown in FIG. 2, the top sheet of the stacked recording sheets 370 contacts the pickup roller 303 by bias force of the spring 309. In such a state, the pickup roller 303 activates and the recording sheet 370 is fed, the recording sheet 370 is fed in the direction of arrow A in FIG. 12.

At this time, in the case where skew generates in the recording sheet 370 and a pressure force acts on the restriction surface 351, since a farthest side part of an extending part from a point of action of force contacts the guide wall of the medium stacking plate 310, skew can be reduced in comparison with the case where only one extending part having similar dimension accuracy is used.

For example, in the case where the sheet leading side (direction of arrow A side) of the restriction surface 351 of the sheet guide 520 shown in FIG. 17 is pressed by a pressure force Fc1 due to skew of the recording sheet stacked on the medium stacking device 502, a front edge 555 h of the side part 555 b of the extending part 555 contacts the guide wall 342 a (FIG. 16) of the medium stacking plate 310, thereby, an incline of the sheet guide 520 with respect to the direction of arrow A can be restricted.

In the same manner, in the case where the sheet trailing side (opposite side of direction of arrow A side) of the restriction surface 351 of the sheet guide 520 shown in FIG. 17 is pressed by a pressure force Fc2 due to skew of the recording sheet stacked on the medium stacking device 502, a front edge 556 h of the side part 556 a of the extending part 556 contacts the guide wall 341 b (FIG. 16) of the medium stacking plate 310, thereby, an incline of the sheet guide 520 with respect to the direction of arrow A can be restricted. Such a mechanism of prevention of rotation of the sheet guide 521 disposed so as to face the sheet guide 520 is similar to the above mentioned mechanism.

As mentioned above, according to the medium stacking device of the embodiment, even if skew is generated in the carried recording sheet, thereby, since an incline of the sheet guides 520, 521 is suppressed with respect to the sheet carrying direction (the direction of arrow A), and the skew of the recording sheet can be diminished. Furthermore, according to the explanation on FIG. 10 of the first embodiment mentioned above, respectively, one of the extending part 556 and the extending part 555 is disposed in the direction of arrow A side and the other is disposed in the opposite side of the direction of arrow A side based on the center in the direction of arrow A of the restriction surface 351. Thereby, the above mentioned effects of the embodiment can be more efficiently obtained regardless of directions of skew.

Note, in the embodiment, the sheet guide to which the two extending parts are provided is shown as an example. However, same effects can be obtained by a sheet guide having two or more extending parts.

Fourth Embodiment

FIG. 18 is an external perspective view illustrating a configuration of a sheet guide 620 (621) in the fourth embodiment.

A medium stacking device employing the sheet guide 620 (621) has a main different point from the image forming apparatus employing the above mentioned medium stacking device 502 of third embodiment shown in FIG. 16. The point is that extending parts 655, 656 (555, 556 in the third embodiment) have a different shape from that of the extending parts 555, 556. Accordingly, the same reference numbers are put to, and explanation and figures are omitted for parts of the image forming apparatus employing these sheet guides 620 (621) that are common with the image forming apparatus 1 of the first embodiment mentioned above (FIG. 1). Different parts of the image forming apparatus from those of the image forming apparatus 1 are intensively explained. Note that since the main configuration of the image forming apparatus of the embodiment is common with the main configuration of image forming apparatus 1 of the first embodiment shown in FIG. 1 other than the medium stacking device, FIGS. 1, 2 will be referred if needed. In this embodiment, the movement restriction parts are realized with two restriction members (extending parts 655 and 656). The number of the restriction members for one movement restriction part is preferably two, but may be three or more.

A shape of the extending part 655, 656 of the sheet guide 620 (621) corresponds to a shape of the rack 355, 356 of the sheet guide 320 (321) shown in FIG. 7 explained in first embodiment other than the tooth parts 355 d, 356 d. Accordingly, when this sheet guide 620 (621) is installed to the medium stacking plate 310, in FIG. 16 explained in the third embodiment, instead of the side parts 555 b, 556 b of respective extending parts 555, 556, like the bias parts 355 c, 355 e and the bias parts 365 c, 365 e in FIG. 4, the bias parts 655 c, 655 e of the sheet guide 620 face and press the guide wall 342 a; the bias parts 656 c, 656 e of the sheet guide 620 face and press the guide wall 341 a; the bias parts 655 c, 655 e of the sheet guide 621 face and press the guide wall 343 a; and the bias parts 656 c, 656 e of the sheet guide 621 face and press the guide wall 344 a.

In the above mentioned configuration, since method of setting recording sheets on the medium stacking device is identical to that of the above mentioned third embodiment, the explanation of the method will be herein omitted.

When a set recording sheet is carried in the direction of arrow A, for example, in a case where a sheet leading side (side of direction of arrow A) of the restriction surface 351 of the sheet guide 621 shown in FIG. 18 is pressed by the pressure force Fc1 due to skew of the recording sheet stacked on the medium stacking device, since forces are respectively led to a direction where the bias part 655 e presses the guide wall 342 a and the bias part 656 e presses the guide wall 341 a, a restrative force Fa4 generated from the bias part 655 e and a restrative force Fa2 generated from the bias part 656 e respectively resist these forces. Thereby, an incline of the sheet guide 620 with respect to the direction of arrow A can be restricted.

In the same manner, in a case where a sheet trailing side (opposite side of direction of arrow A) of the restriction surface 351 of the sheet guide 620 shown in FIG. 18 is pressed by the pressure force Fc2 due to skew of the recording sheet stacked on the medium stacking device, since the front edge part 656 h of the side part 656 a of the extending part 656 functions as a fulcrum, forces are respectively led to a direction where the bias part 655 c presses the guide wall 342 a and the bias part 656 c presses the guide wall 341 a, a restrative force Fa3 generated from the bias part 655 c and a restrative force Fa1 generated from the bias part 656 c respectively resist these forces. Thereby, an incline of the sheet guide 620 with respect to the direction of arrow A can be restricted. Such a mechanism of prevention of incline of the sheet guide 621 disposed so as to face the sheet guide 620 is similar to the above mentioned mechanism.

As mentioned above, according to the medium stacking device of the embodiment, even if skew is generated in the carried recording sheet, thereby, since an incline of the sheet guide 620, 621 is suppressed with respect to the sheet carrying direction (the direction of arrow A), and the skew of the recording sheet can be diminished. Furthermore, according to the explanation on FIG. 10 of the first embodiment mentioned above, respectively, one of the extending part 656 and the extending part 655 is disposed in the direction of arrow A side and the other is disposed in the opposite side of the direction of arrow A side based on the center of the restriction surface 351 in the direction of arrow A. Thereby, the above mentioned effects of the embodiment can be more efficiently obtained regardless of directions of skew.

Note, in the embodiment, the sheet guide to which the two extending parts are provided is shown as an example. However, same effects can be obtained by a sheet guide having two or more extending parts.

Through the specification, a pair of racks (355, 356), a pair of extending parts (555, 556), and another pair of extending parts (655 and 656) are disclosed as the restriction members for the movement restriction parts. However, the restriction members are not necessarily only two components, but may be three or more components which function to regulate the movement of the sheet guide.

In the above mentioned embodiments, applications of the present invention to an electrographic printer are explained. However, the present invention is not limited to the embodiments and may be applied to a multifunction printer (MFP), a facsimile device, a photocopy machine, and the like. In addition, in the above mentioned embodiments, applications of the present invention to manual feed trays are explained. However, the present invention may be applied to a cassette tray, an Auto Document Feeder (ADF), and the like. 

1-14. (canceled)
 15. A medium stacking device, comprising: a medium stacking part that stacks a medium; a first medium restriction part that is positioned movably with respect to the medium stacking part to restrict a position of the medium; a first restriction part that restricts the movement of the first medium restriction part and that includes a first tooth part; and a gear part that engages with the first tooth part, wherein the first restriction part includes a first bias part that biases the first tooth part toward the gear part, and a second bias part that is positioned away from the first bias part in a movement direction of the first medium restriction part and that biases the first tooth part toward the gear part.
 16. The medium stacking device according to claim 15, further comprising: a second restriction part that is positioned away from the first restriction part in a medium carrying direction and that restricts the movement of the first medium restriction part.
 17. The medium stacking device according to claim 16, wherein the first bias part and the second bias part are formed in approximately symmetrical shapes about approximate centers of the first bias part and the second bias part in the moving direction of the first medium restriction part.
 18. The medium stacking device according to claim 17, wherein the first bias part and the second bias part are formed at one end and another end of a region of the first restriction part where the first tooth part is formed in the moving direction of the first medium restriction part.
 19. The medium stacking device according to claim 18, further comprising: a second medium restriction part disposed so as to face the first medium restriction part, wherein when the first medium restriction part and the second medium restriction part are at farthest positions from each other, a rotational center of the gear part is positioned between a first point of action where a bias force of the first bias part acts and a second point of action where a bias force of the second bias part acts.
 20. The medium stacking device according to claim 16, wherein the first bias part includes a first fixed end and a first free end extending from the first fixed end, the second bias part includes a second fixed end and a second free end extending from the second fixed end, and the first and second free ends extend in different directions in the movement direction of the first medium restriction part.
 21. The medium stacking device according to claim 20, wherein the first and second free ends extend away from each other in the movement direction of the first medium restriction part.
 22. The medium stacking device according to claim 16, wherein the first restriction part further includes a first abutment part, and the medium stacking part includes a first support part on which the first abutment part abuts.
 23. The medium stacking device according to claim 16, further comprising: a second medium restriction part that is positioned movably with respect to the medium stacking part to restrict a position of the medium, and a third restriction part that restricts the movement of the second medium restriction part and that includes a second tooth part that engages with the gear part, wherein the first restriction part further includes a first abutment part, and the third restriction part further includes a third bias part that biases the second tooth part toward the gear part, a fourth bias part that is positioned away from the third bias part in a movement direction of the second medium restriction part and that biases the second tooth part toward the gear part, and a second abutment part, and the medium stacking part includes a first support part on which the first abutment part abuts, and a second support part on which the second abutment part abuts.
 24. The medium stacking device according to claim 23, further comprising: a fourth restriction part that is positioned away from the third restriction part in the medium carrying direction and that restricts the movement of the second medium restriction part, wherein the second restriction part includes a third abutment part, the fourth restriction part includes a fourth abutment part, and the medium stacking part includes a third support part on which the third abutment part abuts, and a fourth support part on which the fourth abutment part abuts.
 25. An image forming apparatus, comprising: the medium stacking device according to claim
 16. 26. The medium stacking device according to claim 15, wherein the first bias part and the second bias part are formed in approximately symmetrical shapes about approximate centers of the first bias part and the second bias part in the moving direction of the first medium restriction part.
 27. The medium stacking device according to claim 26, wherein the first bias part and the second bias part are formed at a first end and a second end, respectively, of a region of the first restriction part where the first tooth part is formed in the moving direction of the first medium restriction part.
 28. The medium stacking device according to claim 27, further comprising: a second medium restriction part disposed so as to face the first medium restriction part, wherein when the first medium restriction part and the second medium restriction part are at farthest positions from each other, a rotational center of the gear part is positioned between a first point of action where a bias force of the first bias part acts and a second point of action where a bias force of the second bias part acts.
 29. The medium stacking device according to claim 15, wherein the first bias part includes a first fixed end and a first free end extending from the first fixed end, the second bias part includes a second fixed end and a second free end extending from the second fixed end, and the first and second free ends extend in opposite directions in the movement direction of the first medium restriction part.
 30. The medium stacking device according to claim 29, wherein the first and second free ends extend away from each other in the movement direction of the first medium restriction part.
 31. The medium stacking device according to claim 15, wherein the first restriction part further includes a first abutment part, and the medium stacking part includes a first support part on which the first abutment part abuts.
 32. The medium stacking device according to claim 15, further comprising: a second medium restriction part that is positioned movably with respect to the medium stacking part to restrict a position of the medium, and a second restriction part that restricts the movement of the second medium restriction part and that includes a second tooth part that engages with the gear part, wherein the first restriction part further includes a first abutment part, and the second restriction part further includes a third bias part that biases the second tooth part toward the gear part, a fourth bias part that is positioned away from the third bias part in a movement direction of the second medium restriction part and that biases the second tooth part toward the gear part, and a second abutment part, and the medium stacking part includes a first support part on which the first abutment part abuts, and a second support juuon which the second abutment part abuts.
 33. An image forming apparatus, comprising: the medium stacking device according to claim
 15. 34. The medium stacking device according to claim 15, further comprising: a second medium restriction part that is positioned movably with respect to the medium stacking part to restrict a position of the medium, and a second restriction part that restricts the movement of the second medium restriction part and that includes a second tooth part that engages with the gear part, wherein the first restriction part further includes a first abutment part, the second restriction part further includes a third bias part that biases the second tooth part toward the gear part, a fourth bias part that is positioned away from the third bias part in a movement direction of the second medium restriction part and that biases the second tooth part toward the gear part, and a second abutment part, and the medium stacking part includes a first support part on which the first abutment part abuts, and a second support part on which the second abutment part abuts.
 35. The medium stacking device according to claim 15, wherein when the first medium restriction part is at a farthest position from the gear part, a rotational center of the gear part is positioned between a first point where a bias force of the first bias part acts and a second point where a bias force of the second bias part acts.
 36. The medium stacking device according to claim 16, wherein when the first medium restriction part is at a farthest position from the gear part, a rotational center of the gear part is positioned between a first point where a bias force of the first bias part acts and a second point where a bias force of the second bias part acts.
 37. The medium stacking device according to claim 15, wherein the first bias part includes a first fixed end and a first free end, the second bias part includes a second fixed end and a second free end, the first free end inclines and extends from the first fixed end toward an end side of the first restriction part in the moving direction of the first medium restriction part so as to be separated away from the first tooth part, the second free end inclines and extends from the second fixed end toward an other end side of the first restriction part in the moving direction of the first medium restriction part so as to be separated away from the first tooth part, and the first free end and the second free end extend in directions that are separated away from each other in the movement direction of the first medium restriction part.
 38. The medium stacking device according to claim 16, wherein the first bias part includes a first fixed end and a first free end, the second bias part includes a second fixed end and a second free end, the first free end inclines and extends from the first fixed end toward an end side of the first restriction part in the moving direction of the first medium restriction part so as to be separated away from the first tooth part, the second free end inclines and extends from the second fixed end toward an other end side of the first restriction part in the moving direction of the first medium restriction part so as to be separated away from the first tooth part, and the first free end and the second free end extend in directions that are separated away from each other in the movement direction of the first medium restriction part. 